I rinsed mine weekly, but I had stingrays and South American catfish in my tanks. THe only non cats where a small school of Angels. I pretty much had to rinse my media weekly because plecos, and the pair of sting rays are poop machines.

Ild watch the output on the filter and if it starts slowing, rinse the cartridge/media with tank water. The more good bacteria you have the better. With a single betta once or twice a year depending on the size of the tank.

ETA: If you start to notice a decline in the clarity of water, rinse the media.

ETA ETA:Unless you are on a well, allways rinse with tank water!